The present invention relates to machine vision vehicle wheel alignment systems configured to measure the locations and orientation of the vehicle wheels in a three dimensional coordinate system, and more particularly, to configurations of machine vision cameras and optical targets disposed about a vehicle undergoing an alignment inspection.
Machine vision vehicle wheel alignment systems have been in use by the vehicle service industry for several years. A typical machine vision vehicle wheel alignment system, such as the Series 811 wheel alignment system, configured with the DSP600 sensors manufactured by Hunter Engineering Co. of Bridgeton, Mo. consists of a console unit, cameras, and optical targets. The console unit contains a computer configured with image processing and vehicle wheel alignment software applications, and incorporates various operator interfaces, including a keyboard, a mouse, a printer, and a display device. The cameras are coupled to the computer, and the optical targets are disposed in the field of view of the cameras, typically mounted to the wheels of a vehicle undergoing an alignment inspection.
Commonly, to view the left and right sides of a vehicle, one or more cameras are disposed on opposite sides of the vehicle, each having a field of view encompassing one or more wheels of the vehicle. In alternative configurations, two cameras are provided on each side of the vehicle, each having a field of view encompassing a single vehicle wheel, i.e. a left front, left rear, right front, and right rear wheel, respectively. To facilitate vehicle wheel alignment, optical targets are mounted on the vehicle wheels, and observed by the cameras. The optical targets preferably have predetermined features which are identified in images obtained by the cameras, and which facilitate a determination of the position and orientation of the optical targets. The image processing may take place in the camera modules, in an interface computer, or in the console computer. Once the position and orientation of each optical target is determined, the position and orientation of the associated vehicle wheel can be determined, and correspondingly, the various vehicle wheel alignment angle measurements may be either determined or calculated. These angles typically include camber, caster, and toe angles for each vehicle wheel, the vehicle centerline, and the vehicle rear thrust line.
With conventional machine vision vehicle wheel alignment systems, the positional relationship between each camera utilized in the system is fixed and known, permitting the computer to transform coordinates identified in one camera field of view to corresponding coordinates in a second camera field of view, or to a common coordinate reference system. To establish and maintain the positional relationship between each camera, the cameras in a conventional vehicle wheel alignment system are typically mounted to a common rigid support structure, such as a cross member or frame. If movement of the cameras is required, the rigid support structure ensures that the camera to camera positional relationship is maintained.
For some applications and installations of machine vision vehicle wheel alignment systems, the utilization of a single rigid support structure which is sufficiently large so as to dispose cameras in operative positions to view both the left and right sides of a vehicle is impractical. For example, in drive-through vehicle service bays, a vehicle is typically driven into the bay from one side, and continues out the bay through the opposite side. This prohibits placement of fixed structures in front of the vehicle, unless such structures are suspended from the ceiling. If the ceiling is too high, too low, or not sufficiently stable, this becomes impractical. Correspondingly, in some service “pit” applications, the vehicle is driven onto supporting structures of a runway disposed with an open “pit” or service bay. In such applications, the “pit” or bay may extend around the front of the vehicle to the forward wall of the service area, preventing the placement of fixed or rigid mounting structures in front of the vehicle if there is insufficient clearance between the vehicle and the forward wall.
Prior art systems which utilize independent support structures for cameras displaced to view opposite sides of a vehicle are known. Typically, these systems rely upon calibration procedures carried out prior to measuring vehicle wheel alignment angles. The calibration procedures may utilize one or more cross-looking cameras and/or associated reference targets to determine a positional relationship between each of the camera support structures, which is stored for subsequent use. However, such systems inherently rely upon the assumption that once the positional relationship between the cameras or between the cameras and a corresponding optical target is calibrated, it does not change. Alternatively, the calibration procedures must be repeated after each change in position of the cameras, or change in position of a camera and a corresponding optical target, before vehicle wheel alignment measurements can be determined.
Accordingly, there is a need in the vehicle service industry for machine vision vehicle wheel alignment systems which do not require that all cameras be mounted to a single rigid structure, and that cameras disposed to view one side of a vehicle be movable independently of the cameras disposed to view the opposite side of the vehicle, while maintaining, in real-time, a common reference coordinate system for determining vehicle wheel alignment angles without the need to repeatedly recalculate and store positional calibration data.